The invention relates to a process for the isomerization of paraffins.
For use as gasoline component highly branched paraffins are more suitable than unbranched or moderately branched paraffins having the same number of carbon atoms, since the former have a higher octane number.
For these reasons processes have been developed for the isomerization of paraffins with a lower degree of branching into paraffins with a higher degree of branching. An isomerization treatment of this type can be carried out, for example, by contacting the paraffins to be isomerized with a catalyst in the presence of hydrogen at elevated temperature and pressure, which catalyst contains a layered crystalline aluminosilicate and one or more catalytically active metals or metal compounds such as cobalt, nickel, platinum and palladium. See, for example, H. E. Swift, et al in Ind. ENg. Chem. Prod. Res. Develop., 13 (1974) No. 2, pp. 106-109, where the catalyst is pretreated (reduced) with hydrogen at a temperature of 650.degree. F. (343.degree. C.) before use in a hydroisomerization process.
In view of operational economy it is attractive to use catalysts containing no noble metals. The conversion so far obtained of the paraffins to be isomerized with the use of catalysts of the above type containing no platinum or palladium, however, is not entirely satisfactory, and moreover, the cracking activity of a catalyst of this type is higher than desirable.
It has now been found that the above-mentioned drawbacks do not occur if the catalyst used is a layered metal silicate containing as metals, in addition to aluminum, exclusively nickel and/or cobalt, which layered metal silicate has been treated with hydrogen at a temperature of at least 400.degree. C. before it is used as isomerization catalyst.